Well while i agree with Calabite that keeping it realistic is important, taking economics too far also has its dangers. I know a group that spent an entire session calculating the value of swords they found when they ambushed an evil merchant and then decided to sell his merchandise for profit and i also lived through a Dark Sun campaign where weight calculations were important so you knew how much water you could carry - and it took us a good 45 minutes each session. In the end we could not even carry our money.
So on the one hand realism is important and on the other time is precious, so i try to balance with two rules: fist, if they become rich enough to buy a plus 5 sword early, good for them: the next villain will have a natural armor bonus that will make the battle fair, or will carry an evil shield (so they cannot use it) or will have a spell cast on him/her to make their AC higher. They cannot loot every bonus off the fallen enemy. After all, this IS the third edition! After that, there will be some encounters without treasure, for example a fight with a wild monster or some spirits. Just because the book says that a 6th level encounter has to have THAT amount of treasure, does not mean that a pack of Dire Wolves will have somewhere on them a cache of magical weapons! If the players HAVE to have some treasure, it could a key they need, a guarded map or a piece of knowledge they were looking for.
For example one of the treasures my party found at some point was three bags of holding, as they had stumbled upon the bodies of some tomb looters. So this is how you get out of the weight calculation problems as well!